It is known that, in the motor-vehicle sector, in order to achieve the fixing together of body parts, for example the fixing of an internal finishing panel to the frame of a door or side of the passenger compartment of a vehicle, retaining devices of various types, e.g. snap-engaging or bayonet type, are used.
However, these retaining devices are not suitable for allowing disassembly of the parts connected by them without the risk of causing possible damage and/or without causing the breakage of the retaining device, in particular those devices of the type able to be assembled by means of snap-engagement.
The only known retaining device which can be reused and is suitable for allowing also frequent assembly and disassembly without the risk of damage is the screw. However, connecting together body parts by means of screws would be costly and would slow down the operations of assembly of the parts to be joined together owing to the time needed to perform screwing of the screws.